1. Field of the Invention
This invention relates to aircraft instruments, and more particularly to electronic flight instrument housings.
2. Description of the Prior Art
The advent of the dedicated microprocessor and its associated digital electronics has introduced novel heat dissipation requirements into the design and manufacture of electronic flight instruments. In prior art analog electronic flight instruments, the electronics "ran" cooler so that generally conventional packaging techniques could be employed. In a rate-of-climb indicator, for example, the internal structure of the instrument is typically secured to a front bezel, and the entire assembly is simply enclosed in a one piece closed end can type of housing. The end piece of the housing is attached to the internal structure of the instrument using suitable shims or the like to compensate for any front-to-back tolerance build-up or accumulation and to facilitate heat dissipation. Another prior art thermal management technique is the use of relatively thick metallic support plates and structures which served as heat sinks for the internal electronics. This technique adds not only expense, but more importantly it adds to the total weight which is highly undesirable in flight instruments.
It should be noted that in the thermal design of an electronic flight instrument housing, there is a need for close, intimate and tight physical contact between the housing and the thermal conducting elements or heat sinks associated with the heat generating electronics. In actual practice, however, this physical contact is not as easily achieved as it may first appear, especially in view of the manufacturing tolerance build-up or accumulation which may cause misalignment during assembly. Moreover, there is an additional need for sealing flight instruments to satisfy the humidity and salt evironmental test requirements, and this sealing requirement prohibits the simple tolerance build-up compensation method of slotting the screw holes in the housing.
Accordingly, there is a need for an electric instrument housing that is both efficient to assemble and that is well adapted to dissipate the heat generated by the digital electronics associated with a dedicated microprocessor.